Muffler sizing help for a 2000 chevy silverado 1500 2wd regular cab.?

i have a silverado and im trying to add a glass pack(muffler that makes your vehicle sound louder and increases performance). does anyone know the size muffler i should get. ive had people say its a 2 1/2 inch pipe and others say its a 2 3/4 intch pipe. i mesured it and i got 2 3/4 which creates problem. i absoloutly cannot find a muffler that has a 2 3/4 inch inlet. does anyone know if i can fit a muffler with a 2 1/2 or a 3 inch muffler on it. what can i do.